Biolutninescence 671 



ase, luciferin, or possibly an unidentified third constituent which is the actual 

 light-emitter. Furthermore, some characteristics of the bioluminescent reac- 

 tion so differ among species, for example between Cypridina and fireflies, 

 that it would appear that a final detailed explanation for one would prob- 

 ably not be a complete explanation of the other. 



There is very good evidence that phosphate is liberated during the lu- 

 minescent reaction.^" This suggests that energy-rich phosphate bonds are the 

 sources of the eneroy liberated, as has been demonstrated for muscle meta- 

 holism. 



Variations in electrical potential in light organs have been described as 

 accompanying light production in some fireflies.-^''- ■'^- •^'^ In adults, which 

 show a flickering light, there is a rhythmical potential variation; in larvae, 

 larking a flickering character of light, there is a single, long-duration, po- 

 tential variation. The former type of response is correlated with the pres- 

 ence of tracheal end-cells; the latter, with their absence. 



The Control of Bioluminescence. Among animals the production of light 

 is typically not a continuous process. Light is usually produced intermittently 

 in response to external stimuli. This fact is of such generality that, when an 

 animal appears to have continuous luminescence, it can usually be assumed 

 that this is the result of the presence of symbiotic, pathogenic, or transient 

 luminescent bacteria within or upon that animal. 



The means of control of light production in animals are fundamentally 

 of three types. The first two are observed in extracellular luminescence. In 

 those instances where luminescent materials are expelled from a photogenic 

 sac into the surrounding sea water on stimulation (as in the cephalopod, 

 Heterotetithis, the ostracod, Cypridina, and the shrimp, Acanthephyra'), the 

 control is indirect and operates by means of typical neuromuscular mechan- 

 isms. On the other hand, a slightly different situation obtains in those organ- 

 isms which can secrete a luminescent slime over the surface of the body. 

 Such animals include the luminescent earthworms, Chaetopteriis, myriapods, 

 many coelenterates, and the clam, Pholas. In these there is a control of a 

 secretory process by direct nervous, or possibly also, in some cases, endocrine 

 excitation. The third general type of control applies to those numerous ani- 

 mals where the luminescence is an intracellular phenomenon. This is ob- 

 viously the situation in such well-known animals as Noctihica, the insects, 

 and certain fishes. Here we have to do with some mechanism whereby ex- 

 citation of the luminescent cell results in the contained photogenic sub- 

 stances being permitted to interact. The interaction may possibly come about 

 either through rapidly making small quantities of one of the two essential 

 photogenic reactants available to the other within the cell, or through tem- 

 porarily rendering the milieu favorable for the luminescent reactions. The 

 latter might occur through control of oxygen, water, hydrogen ions, etc. We 

 can at present do little more than speculate on the means by which the ani- 

 mal can, in response to stimuli, give \'ery brief and intense flashes of light 

 which vie in rate of development and decline of intensity with the best ol 

 incandescent lamps. 



In multicellular organisms the flashing is typically associated reflexly with 

 tactile or photic receptors. The reflex pathways may involve the ner\'ous 

 system alone, or both ner\ es and endocrines. In the coelenterate. Reuilln, the 



